The stability of morphine in isobaric and hyperbaric solutions in a drug delivery system

Intrathecal preparations of morphine for use in intractable pain must contain no preservatives. They are generally formulated in saline (isobaric) or dextrose (hyperbaric) which raises questions of stability. The behaviour of morphine in hyperbaric and isobaric solutions stored in a reservoir for implantation has been examined and the effect of temperature and the time of contact of morphine with the different components of the reservoir as well as the sterilization procedure have been investigated. The best stability was observed with a hyperbaric solution in which there was 15 to 20 times less pseudomorphine than in the isobaric solution, which was found to contain 1% pseudomorphine after 1 month of storage at 37 degrees C in the reservoir. Similar solutions stored in ampoules did not degrade.